Moulds of the above-mentioned kind and a method for producing them are already known, for example through the Swedish published Patent Application No. 76 00895-2 (GB No. 1 541 446). This known invention has also begun to be used in practice for the production of moulds in plastics moulding tools and, within this field, has represented a considerable technical advance in comparison with moulds produced in a conventional manner, primarily because the production costs are lower but also because they can be produced much more quickly which in many cases is of decisive importance.
It is also known to dispose cooling passages in moulding tools with the object of causing the products which are to be moulded in the tool to solidify more quickly and/or to bring about a controlled solidifying process. Conventionally, these cooling passages are produced by drilling in the tool or the material of the tool. For natural reasons there are great limitations to this conventional technique. For example, it is not possible to drill curved cooling passages; only straight passages or passages composed of straight portions. Only exceptionally can the passages be placed so that they "cover" all the moulding surfaces of the tool or even considerable parts of these, from the cooling point of view. Another disadvantage of cooling passages which are produced in conventional manner by drilling is that their walls do not have any better resistance to corrosion than the resistance of the material of the tool to corrosion. This applies both to moulding tools produced conventionally and to moulding tools of the kind given in the definition of the technical field of the invention. During use of the tool, the cooling water can therefore corrode the cooling passages so that these become wholly or partially blocked. Admittedly, this can be counteracted in certain cases by means of corrosion inhibitors or by lining the cooling passages with a more corrosion-resistant material. There are great limitations to both these possibilities, however, and in all circumstances they involve complications which are such serious complications when it is a question of lining, that this method is scarcely realistic in practice.
A specific complication in producing the composite article given in the technical field of the invention results from the tendency of the matrix metal to shrink in connection with the solidification. Normally, the solidification does not take place simultaneously in all parts of the porous body but first in the parts where the cooling is greatest, the shape and structure of the body being stabilized in these parts. Through the shrinkage, matrix metal which has not solidified can be sucked away to a certain extent from other parts of the porous body, inter alia from surface portions which have not yet been stabilized. As a result, the sintered material projects in relief in these surfaces so that the surfaces are rough. In certain cases, this may be fatal, particularly if these surfaces are to constitute moulding surfaces in a moulding tool with high requirements regarding accuracy of dimensions and fineness of surface. In the majority of cases, the problem can admittedly be solved by finishing in the form of grinding and/or surface coating, but it is desirable not to have recourse to this, if possible.